Fire alarm systems are often installed within commercial, residential, or governmental buildings, for instance. Examples of these buildings include hospitals, warehouses, schools, hotels, shopping malls, commercial and governmental buildings, and casinos. The fire alarm systems monitor for an existence of fire conditions, such as smoke or heat, and alert occupants when the fire conditions are detected.
Fire alarm systems typically include notification appliance devices for alerting occupants of the potential fire. Notification appliance devices include notification units such as horns or strobes. The notification units generate alert signals (e.g., audible signals or visible signals) for indicating an alarm (i.e., potential fire) to occupants.
Fire alarm systems also include initiation devices that can detect fire conditions or be manually activated. One type of initiation device is a detector device that includes a sensor unit for detecting the existence of fire conditions (i.e., smoke or heat). The sensor unit can be a smoke sensor, a heat sensor, a flame sensor, or the like. Another type of initiation device is a notification/detector combination device that includes a notification unit and a smoke/heat sensor unit. Still another type of initiation device is a manually activated unit such as a fire alarm box/pull station. The fire alarm box/pull station can be manually actuated by pulling a handle and/or pushing a bar. For purposes of this discussion, a manually activated unit includes any device that is actuated by a human person. For example, devices designed to be actuated by a person who may not have use of their hands. (note: ADA compliant devices)
System controllers of the fire alarm systems monitor the initiation devices and activate the notification appliance devices. For example, when fire conditions (i.e., smoke or heat) are detected by the initiation devices (e.g., detector devices and notification/detector combination devices), the initiation devices send alarm signals to the system controller. The system controller responds to the alarm signals by activating the notification appliance devices to generate the alert signals to indicate an alarm (i.e., alert occupants of potential fire).
System networks connect the system controllers to the initiation devices and notification appliance devices. The system networks typically include at least one common pair of lines, also known as a loop. Several initiation devices and notification appliance devices can be wired to this common pair of lines that extend from the system controller. The system controller provides power to and communicates with the initiation devices and notification appliance devices on the common pair of lines. Typically, the system controller has a power source such as a DC power unit to supply power on the common pair of lines. This DC power unit supplies power at a fixed voltage and is limited to providing a maximum current.
The notification appliance devices have a communication mode and an activation mode. In the communication mode, the notification appliance devices perform basic operations such as communicating with the system controller (e.g., respond to group polling) while the notification units are kept inactive. In the activation mode, the notification units are activated (i.e., turned on) causing generating of the alert signals.